Inorganic inert fillers and polymeric materials are often used in admixture with one another. Depending on the ratio by weight of filler to polymeric material, properties can be attributed to the end product obtainable from such a mixture that would be very difficult or even impossible to achieve using a material which consisted of only one of the components of the mixture (i.e. only polymer or only filler). The combination of inorganic inert filler and polymers is often aimed at and used not least because both materials have very different property profiles of which the combination is not only desirable but actually necessary for many applications.
Fillers which generally consist of a number of individual loose filler particles are often chemically inert to the environment around them. Because of this, filler particles can often only be formed/shaped together with a binder. Suitable binders are, for example, organic and inorganic binders. One exception to this are fillers which are capable of setting to form solid materials by reacting with a reactant present in the surrounding environment. Examples of such fillers are gypsum in the form of anhydrite and various lime compounds which are capable of curing by reacting with water or carbon dioxide from the surrounding air.
Whereas the self-setting fillers mentioned above generally cure to form brittle hard materials, a distinctly broader spectrum of physical and chemical properties can often be achieved by replacing the inorganic materials with polymers. However, disadvantages of using polymers only generally include increased production costs by comparison with inorganic materials and their lower hardness and chemical resistance, particularly in regard to fire resistance and flameproofing.
In this connection, the building supplies industry in particular has a steadily increasing demand for new materials which combine the positive properties of fillers, such as their chemical resistance, their resistance to heat, their availability in large quantities and their low price, with those of the polymers. The demand ranges from surface coating compositions or adhesives, which are generally applied as a thin layer to surfaces of various kinds, through surfacing and sealing compounds to plastics of the type used, for example, as a sheathing for power cables or as water conduits.
For example, Wirsching, Hüller, Hufmann and Pürzer describe the use of fillers of WDP gypsum in ZKG INTERNATIONAL, No. 5, 1995 (Vol. 48), pp. 241–256 (Bauverlag GmbH). The article in question describes in particular the use of WDP gypsum from coal-fired power stations in adhesives, paints and plastics. Before being used as a filler, the gypsum is finely ground so that it has a mean particle diameter of about 8 to 12 μm and the upper cut of the particle diameter is at about 25 to 50 μm.
JP 76-139114 relates to the use of WDP gypsum as a pigment in coating compositions. This document describes a composition of titanium dioxide, WDP gypsum, aluminium silicate, ethylene/vinyl acetate copolymer, polyvinyl acetate, thickener and water as a white emulsion which is suitable as a coating composition.
Filler-containing polymer materials are often marketed and processed in the form of aqueous dispersions. Unfortunately, such materials frequently have serious disadvantages during and after processing. Firstly, the viscosity of the dispersions often cannot be adjusted to a value suitable for processing. Secondly, after processing and generally after drying, the filler-containing polymer material applied undergoes a distinct change in volume in relation to its volume at the time of application. This change in volume can often correspond to the extent to be expected as a result of evaporation of the water present in the dispersion.
Behavior such as this (often referred to as “shrinkage” or “contraction”) is undesirable, above all for filler-containing polymer dispersions which are supposed to perform a “filling” function. Thus, in the case of surface coatings for example, importance is often attributed to the levelling of any structural unevenness of the substrate. Surfacing or sealing compounds, for example, are expected to fill the void to be sealed or filled—even after drying of the compound introduced—to the full extent to which the dispersion was originally introduced.
In addition, the contraction of surfacing compounds frequently leads during drying of the compound to the formation of cracks therein which, besides the generally noticeable visual disadvantages, often represent starting points for the penetration of corrosive compounds or moisture. The visual impression and the stability of the region thus filled are often drastically impaired as a result.
Filler-containing polymer materials are often used as adhesives, more particularly emulsion-based adhesives. Unfortunately, many adhesives of this type lack elasticity which is often a disadvantage to the stability of the adhesive bond under stress.